1. Field of the Invention
The present invention relates to a power steering control device, a method therefor, and a program therefor, and particularly to a power steering control device capable of detecting an abnormality of a reference voltage of an electric power steering control unit, a method therefor, and a program therefor.
2. Related Background Art
An electric power steering device using a torque of an electric motor has been utilized as an assist steering device for an automobile. The power steering device is constituted to have: a torque sensor that detects a steering wheel operation by a driver and automotive movement; an electric power steering control unit (ECU) that calculates an assist steering force in accordance with a detection signal from the torque sensor; an electric motor that generates a rotating torque in accordance with an output signal from the ECU; a reduction gear that transmits the rotating torque to a steering mechanism; and the like.
In the power steering device as constituted above, when the driver steers a steering, a torque is applied to the torque sensor, and then, a torque signal in correspondence with the torque strength is output to an A/D converter in the ECU. The ECU calculates a steering assist torque in accordance with the A/D converted torque signal, and the steering assist torque is given to the steering by means of the electric motor.
The above-mentioned torque sensor has two output signals, that is, a main torque signal and a sub torque signal, and is set to exhibit a cross characteristic in which the total voltage of those signals is a constant voltage (for example, 5 V). That is, in the case where the torque is not applied to the steering, the main torque signal and the sub torque signal each have a torque neutral voltage of 2.5 V; on the other hand, in the case where any torque is applied to the steering, the main torque signal and the sub torque signal fluctuate in opposite directions with the torque neutral voltage of 2.5 V as a reference.
Further, a reference-voltage generator circuit for the torque sensor is provided in the ECU so as to detect the torque neutral voltage with accuracy. In general, a power supply voltage for driving the torque sensor is easy to fluctuate due to other electric circuits mounted in a car and environmental variation such as temperature variation. Moreover, the A/D converter has a predetermined detection voltage error. Thus, even if the torque neutral voltage of 2.5 V is precisely input to the A/D converter from the torque sensor, the ECU performs misdetection of the torque.
From the above reasons, the reference-voltage generator circuit for the torque sensor is provided, and also, a reference voltage from the reference-voltage generator circuit is used as a reference voltage of the A/D converter. Accordingly, the conversion error of the torque neutral voltage in the A/D converter is eliminated. Further, the same reference voltage is given to the torque sensor and the A/D converter. As a result, even if the reference voltage in the reference-voltage generator circuit slightly fluctuates, the A/D converted neutral voltage is difficult to fluctuate.
Further, the total voltage of the main torque signal and the sub torque signal from the torque sensor is the constant voltage of 5 V. Thus, monitoring the voltage enables detection of an abnormality of the torque sensor.
However, in the above-described device, although the reference voltage from the reference-voltage generator circuit is used as the reference voltage for A/D conversion, monitoring the reference voltage itself is not performed. Therefore, it has been such that an abnormality of the reference-voltage generator circuit cannot be detected even if the reference voltage largely fluctuates due to the abnormality of the reference-voltage generator circuit. Further, monitoring the reference voltage from the torque sensor is also used for detection of other fault modes in many cases, and thus, a normal value of the reference voltage needs to be set in a wide range. Therefore, even if the abnormality occurs in the reference-voltage generator circuit, it may be judged that the reference voltage is in a normal range. For example, in the case where the reference voltage of the torque sensor is close to a limitation on the normal value, there may be a difference between right and left toward steering forces detected by the torque sensor.
Note that a reference-voltage generator circuit for a torque sensor is disclosed as a conventional power steering control device in JP 2001-088728 A. The reference-voltage generator circuit is used not only for a reference of a torque neutral voltage of the torque sensor but also for a reference voltage of an A/D converter in an ECU. However, monitoring a reference voltage of the reference-voltage generator circuit is not performed. Therefore, it has been difficult to perform a fail safe process in accordance with a state of the reference-voltage generator circuit.